Air travel today is extraordinarily safe. Despite the high profile downings of MH370 and MH17, aviation magazine Flightglobal found 2014 to be the safest ever year of air travel. But natural events, such as the Icelandic ...

Gravity, one of the four fundamental forces of nature, appears reassuringly constant across the Universe, according to a decades-long study of a distant pulsar. This research helps to answer a long-standing question in cosmology: ...

Physicists at the University of York have revealed a new understanding of nucleosynthesis in stars, providing insight into the role massive stars play in the evolution of the Milky Way and the origins of the Solar System.

Although global concentration of greenhouse gases in the atmosphere has continuously increased over the past decade, the mean global surface temperature has not followed the same path. A team of international reseachers, ...

A satellite experiment to study cosmic rays and the solar wind that was devised by school students is now successfully collecting data in space. LUCID, the Langton Ultimate Cosmic ray Intensity Detector, uses particle detectors ...

Sunlight

Sunlight, in the broad sense, is the total spectrum of the electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon. Near the poles in summer, the days are longer and the nights are shorter or non-existent. In the winter at the poles the nights are longer and for some periods of time, sunlight may not occur at all. When the direct radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and heat. Radiant heat directly produced by the radiation of the sun is different from the increase in atmospheric temperature due to the radiative heating of the atmosphere by the sun's radiation. Sunlight may be recorded using a sunshine recorder, pyranometer or pyrheliometer. Sunlight takes about 8.3 minutes to reach the Earth. The World Meteorological Organization defines sunshine as direct irradiance from the Sun measured on the ground of at least 120 watts per square metre.

Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux, which includes infrared, visible, and ultra-violet light. Bright sunlight provides luminance of approximately 100,000 candela per square meter at the Earth's surface.

Sunlight is a key factor in photosynthesis, a process crucially important for life on Earth.